Radio system



I. WOLFF RADIO SYSTEM June 1, 1937.

Filed April 26, 1934 3 Sheets-Sheet l [AWE/V706: x 24 95 7/ L WTTO/EWEK June 1, 1937.

I. WOLFE- RADIO SYSTE-M Filed April 26 1934 3 Sheets-Sheet 2 1 Jay INVENTOB y m WTTOBWEE Patented June 1,1937

RADIO SYSTEM Irving Wolff, Merchantvllle, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application April 26, 1934, Serial No. 722,471

8 Claims.

My invention relates to radio systems and particularly, to systems which utilize electromagnetic energy having such a high frequency that.

' Figure 3 installed at a landing field; and

t it may be transmitted in the form of a beam. 5 An object of.my invention is to provide an improved method and means for modulating electromagnetic energy.

A further object of my invention is to provide an improvedmethod and means fortransmitting' '0 I produce one modulation in one part of a radio beam and another modulation in another part thereof by intercepting different parts of the beam by means of modulating devices such as tubes containing an ionized gas. Thus, for ex- 25 ample, in a radio beam which is cone shaped,

the central portion of the beam may be modulated in accordance with one signal while the outer portion of the beam is simultaneously modulated in accordance with a different signal.

30 In accordance with oneembodiment of my invention, I modulate adjacent sections of a radio beam by signals differing in frequency whereby a sharply defined path is provided which may be followed by an air craft or the like. If the 85 source of the beam is located at a landing field, aiid projected upwardly at an angle to thefield, anair craft equipped with suitable receiving apparatus may follow down the beam-to make a landing.

-40 Other objects, features and advantages of my invention will appear from the following description taken in connection, with the accompanying drawings, in which l Figure .1 ,is a. schematic diagram of one em-' bodiment of my invention showing a side view of the modulating device;

- Figure '2 is a schematic diagram of a portion of the apparatus illustrated in Figure 1 showing an 50 end view of. the modulating device;

perspective, ofan air craft landing system constructed in accordance with one embodiment of my invention; l

5 Figures 4 and .5 are diagrams which are redevices may be employed, such as shuttersor screens, I prefer to employ an ionized gas. de-

Fi'gure 3 is a schematic diagram, partly in ferred to in explaining the operation of the apparatus shown in Figure 3;

Figure ii is a view showing the apparatus of suitable means for producing a beam of electromagnetic energy. the apparatus illustrated con sisting of a generator of high frequency radio energy indicated at i which is connected. to a dipole antenna 3 positioned in a parabolic rcflector 5. In accordance with my invention, I 15 intercept difierent portions of the radio beam with different modulating devices whereby the said portions of the beam may be modulated independently. While various types of modulating vice of the type described and claimed in U. S. Patent No. 2,047,930, which issued on July 14, 1936, to Ernest G. Linder, and is assigned to the same 'assignee as this application.

As shown in Figures 1 and 2, two.modulating devices 1 and 9 are utilized, one beingpositioned at the center of the radio beam to modulate the central part of the beam and the other being 130- sitione'd to modulate the outer part of the beam. The central modulating device 1 comprises a long tube I I filled with gas at a low pressure and bentinto a spiral to form a circular sector disc of gas,

The other modulating device 9 consists of a long gas.

Electrodes l5 are provided at the ends of the tube II and connectedto a suitable voltage supply such as a battery l1 through the secondary winding IQ of atransformer 2|, the voltage of the battery being high enough to maintain the gas in the tube ii in an ionized condition. The primary winding 23' of the transformer 2-lis connected through a battery 25 toa microphone 21 whereby the voltage applied to the electrodes l5,

a and consequently the ionization of the gas, may

be varied in accordance with speech.

In the same way, the ionization of the gasin the tube l3 may be varied by means of a varyo I ing voltage applied to'electrodes 29 provided at the ends thereof through a circuit including a second microphone 3|, a transformer 33 and a battery 35. As fully explained in the above mentioned Linder docket, the radio beam is modulated in accordance with the variations in the ionized gas as the beam passes therethrough. The microphones are merely illustrative; they may, of course, be replaced by any suitable sources of modulating energy such as constant frequency generators.

It will be apparent that if different signals are impressed upon the two modulating circuits, the above described apparatus will produce a 'radio beam having one modulation P on its central portion .and a different modulation Q on its outer portion, as indicated in Figure 1. Thus, if desired, two conversations may be transmitted over the .same radio beam simultaneously by positioning one receiver to pick up energy from the central portion of the beam and another receiver to pick up energy from the outer portion of the beam.

It is'well known that, depending upon the relative size of the reflector compared to wave length, and also depending upon the shape of the reflector, the radio beam travels a certain distance from the reflector, without spreading much and then goes out in the form of a cone. While the modulating devices may be positioned at any point in the radio beam, they are preferably positioned at a point where'the beam has spread out into theform of a cone. Also, the surfaces of the modulating devices which are impinged on by the radio waves should either correspond as nearly as possible to the wave front of those waves, or they should have a very slight converging action. The shape of the strata of ionizing gas also should lie along wave fronts for best results in order to keep from distorting the beam.

Referring to the airplane guiding and landing equipment shown in Figure 3, it includes a generator of high'frequency radio energy indicated at 31 having its output connected to a dipole antenna 39 positioned in a parabolic reflector 4| whereby a beam of radio energy may be radiated.

Two modulating devices 43 and 45 are positioned in the path of the beam for putting one modulation on the right-hand half of the beam and a different modulation on the left-hand half of the beam. In practice, the two modulating devices usually will' be positioned in substantially the same plane. Each modulating device consists of a long tube filled with gas at a low pressure and having electrodes 41 at each end for ionizing the gas.

The modulating device 43 is connected through a battery 49 to the secondary winding 5| 'ofa transformer 53. The primary winding 55 of the transformer 53 may be connected through a switch 51 either to a generator 59 which produces a signal havinga constant frequency Nz or to a generator 6| (which may have a 500 cycle output) and a keying device 63 by means of which the letter A may beimpressed upon one half of the beam.

The modulating device 45 is connected through a battery 55 to the secondary winding 51 of a transformer 69. The primary winding H of this transformer may be connected through a switch 13 either to agenerator |5 which produces a signal having a constant frequency N1 or to a generator 11 .(which may have a 500 cycle output) and a keyingdevice 19 which will put the signal N orrthe other half of the beam.

The keying devices 63 and 19 are operated by synchronism by a motor 8| as indicated by the dotted line 83 whereby the A and N signals are interlocked in the same manner as in the well known radio beacons. That is, the right-hand and left-hand portions of the radio beam are so modulated that if a signal is picked up on the right-hand side of the beam, an A signal is heard, while if a signal is picked up on the lefthand side of the beam, an N signal is heard. However, if a signal is picked up at the center of the beam, a continuous tone is heard due to the overlapping of the N and A signals. From the above description, it will be apparent that the beam has one modulation thereon on one side of a vertical plane passing through the center of the beam and another modulation thereon on the opposite side of the said plane.

Additional modulations are put on the upper and lower halves of the radio beam by means of modulating devices 85 and 81 similar to the modulating devices 43 and 45. The upper modulating device 85 is connected through a battery .89 and a transformer 9| to a signal source |9| of constant frequency M1. The lower modulating device 81 is connected through a battery I03 and a transformer I95 to a signal source I01 of constant frequency M2. Thus, after the beam has been modulated by the first modulating devices 43 and 45: it is again modulated, the upper half of the beam being modulated by the signal M1 and the lower half of the beam being modulated by the signal M2. v r

With the switches 51 and I3 moved to their upward positions to connect the sources 59 and 15 to the modulating devices 43 and 45, respectively, the radio beam is modulated in the manner indicated in Figure 4. It will be seen that the upper right-hand quarter of the beam (looking into the reflector 4|) is modulated by the signals N2 and M1; that the lower right-hand quarter is modulated by the signals N2 and M2; that the lower left-hand quarter is modulated by the signals N1 and M2; and that the upper left-hand quarter is modulated by the signals N1 and M1.

With the switches in the position illustrated in Figure 3 to connect the 500 cycle signal sources 6| and 11 to the modulating devices 43 and 45,

respectively, through the keying apparatus, the' beam is modulated in the manner shown'in Figure 5. It will be seen that the upper right-hand quarter of the beam is modulated bythe signals A and M1; that the lower right-hand. quarter is modulated by the signals A and M2: that the lower left-hand quarter'ls modulated by thesignals N and M2; and that the Upper left-hand quarter is modulated by. the-sign is N and M1.

While the above described appalatus may be employed for' guidingair craft ini horizontal flight, it is most useful when employed for guiding air craft to a landing. In Figure 6, the apparatus is shown installed for this purpose. In

Figures 3 and 6, similar parts are indicated by the same reference numerals. As indicated in Figure 6. the transmitting and modulating apparatus is preferably -mounted upon a turntable "I99 located in a pit in the landing field. The

transmitting apparatus at approximately the center ofv the field, the beam may be pointed into the direction of the wind at any time by rotating the turntable I09. The manner in which the p beam is employed for making blind landings will be better understoodafter a consideration of the receiving equipment.

The receiving equipment shown in Figure 7.

IH and from the amplifier I2I to a plurality of mechanical filters I25, I21, I29, and I3I. primary of the transformer II9'is preferably slz unted. by a radio frequency by-pass condenser I 3. v

Each mechanical filter comprises a driving coil D, a pick-up coil P and a tuned reed R. Filters- I and I21 are tuned to the frequencies Ma and M1, respectively, whereby filter I25 will pass the signal picked up from the lower half of the radio beam, while thefilter I21 will-pass the signal picked up from the upper half of the beam.

An indicating instrument I33 is provided which comprises two pivoted pointers I35 and I31, the pointer I35 being connected to opposing solenoids I39 and I H whereby the position of the pointer I depends upon the current flowing through their coils. The pointer I31 is connected'to opposing solenoids I43 and I45 so that its position, also, is determined by. the value of the 35 current flowing through thesolenoid coils.

The coil ofsolenoid I39 is connected to the pick-up coil P of the filter I25through a rectifier I41 while the coil of solenoid MI is connected.

to the pick-up coil P of filter I21 through a rectifier I49. v

If the solenoids I39 and I have the same amount of current flowing therethrough, the metadle I35. will intersect a circular marking I5I on the instrument dial. Therefore, if an air craft is 45 following 'down a radio beam at the center of the beam, the needle I35 will bein a horizontal'position intersecting the circle I5I since the signals Mian'd M2 picked up by the air craft will-be of equal magnitude.

Referring now to the circuit for controlling the needle I31, the coil of solenoid I43 is connected to the pick-up coil P of filter I29 through a rectifier I53 while the coil of solenoid I45 is connected to the pick-up coil P of filter I-3I through a 55 v rectifier I55, Assuming that the beam is being "modulated in the manner indicated in Figure 4, if an air craft is in the center of the beam, the needle 131 will be in a vertical position to inter 58051318 circleflil, since the received signals N1 and N: are of equal magnitude. If theair craft moves to one side of the center of the beamithe needle I31 will be deflected away. from'tlfe circular, marking III and the pilot will know that he must correct his course. i

'65 In utilizing the aboverdescribe'd system; with;

beam as it passes through two modulating devices in succession. For example, as the beam passes through the device 45 it is modulated by the signal having frequency N1, and,'as it next passes through the device 51, it is not only modulated by the signal having frequency Ma but it is so modulated as to include signals of the frequencies M2+N1 and Mz-N1. 5

However, by properly choosing the modulating frequencies N1, N2, M1 and Ma, no sum or difference frequency will be equal to a modulating frequency and,,theref.ore, the sum and difierence frequencies cannot pass through the four me- 10 chanical filters to efiect a false operation of the. indicator. While various frequency combinations may be chosen for satisfactory operation, the following are given by way of example: N1=50 cycles per second, N2=75 cycles per second; 15 M2=175 cycles per second, and Mi=200 cycles per second.

Byreferring to Figure 4 it will be seen thatthe possible frequency combinations are MaiNi. Mil-N1, MziNz, and MlifNI- quency values specified above, none of these frequency combinations is equal to one of the modulating frequencies. v

The receiving apparatus shown in Figure 8 is designed for use with a beam modulated in the 25. manner shown inli'igure 5. The receiver preferably comprises the usualdipole antenna I 51, which may be positioned in a parabolic reflector- I59, and a detector I6I' for demodulating a radio. beam signal. The demodulated signal is supplied 30 through a transformer I63 to an audio frequency amplifier I65 and through a filter I51 to a pair of headphones I69; The filter I51 is designed to pass the N and A signals having the 500 cycle tone, but to eliminate the frequencies M1 and Ma. 3 Therefore, in the headphones I59 only the N and Akignals will be heard.

The vertical position of theair craft on the beam is'indicated by the position of a disc I" which preferably is mounted upon the face of any,

'blind fiyinginstrument such as the well known Sperry artificial horizon. The artificial hori- ,zori, which is illustrated, comprises a movable bar I13 and a stationary indicating device I15.

representing an airplane, the indicating device 45 being the upper portion of an upright I11. -The position of the bar I13 with respect to theindi- -cating airplane I15-shows the angle, of the airplane with respect to the"horizontal. Also, the angle of the bar I13 indicates whether the wings 5 ofthe'planejare level. By combining with this either up or down by meansof a horizontal. arm 6 I8! pivoted at the point I33 and actuated by,

means of solenoid .coils I and I91. The coil.

I is connected to the output of the amplifier I55= through a rectifier I89 and-a mechanical filter. 'I9I tuned'to frequency Ma. I81 connected to the output of the amplifier I65'through arectifier I93 and a mechanical filter I95 tuned to the frequency' M1.

'If the aircraft is half way between {the upper' and lower portions of the radio beam, the signals 7 M1 and Ma will be of equal intensity and the indicating disc I1 I will be positioned in the center of a circular marking I91 on the upri'ght'lffl. If the air craft moves into the lower half of the beam, for example, the indicating disc I1I wi1l 7 Using the fre-v 20' The solenoid coil r move below the center of the circle I91 and the pilot will know that he must pull the plane up to reach the center of the beam.

With the system shown in Figure 8, the pilot 5 determines his horizontal position by means of the signals appearing in the headset I69. If he receives either an A or an N signal, he knows that he is either to the right or to the left of the center of the beam. He then corrects his course until he hears a steady tone and, if the indicating disc Ill is in the center of the circle I 91 at the same time, he knows he is in the center of the beam and in position to make a good landing.

-Various other modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1. In a system for signalling with electromagnetic energy having a radio frequency, means for radiating said energy, a plurality of modulating devices, each containing a gas capable of being ionized, one of said devices being positioned to intercept a portion of said radiated energy, another of said devices being positioned to intercept a different portion of said radiated energy, and means for varying the ionization of said gas in accordance with desired signals.

2. In a system for guiding an air craft, means for producing a beam of radiant energy at an angle to'the vertical, means for modulating an upper portion of said beam in accordance with one signal, means for modulating a lower portion of said beam in accordance with another signal, receiving apparatus on said aircraft including means for demodulating said beam portions whereby said two signals appear in the output of said receiving apparatus, a visual indicating device, means for moving said indicating device in one direction in response to one of said signals and means for moving said indicating device in the opposite direction in response to the other of said signals.

3. In a system for guiding an air craft, means for producing a beam of radiant energy at an angle to the vertical, means for modulating a portion of said beam in accordance with a first signal, said portion being below a plane which passes through said beam and which is substantially parallel to the axis thereof, means for modulating a portion of said beam above said plane in accordance with a second signal, means for putting two additional modulations on said beam, one of said additional modulations being put on a portion of said beam located on one side of a substantially vertical plane and the other additional modulation being put on a portion of said beam on the other side of said, vertical plane, receiving apparatus on said air craft, said apparatus including means for demodulating said beam portions whereby said signals and additional modulations appear in the output of said receiving apparatus, an indicating device, means for actuating said indicating device in one manner in accordance with said first signal, means for actuating said indicating device in a different manner in accordance with said second signal, and means for producing an audible signal in accordance with said additional modulations.

'4. In a system for guiding an air craft, means for producing a beam of radiant energy at an angle to the vertical, means for modulating a portion of said beam in accordance with a first signal, said portion being below a plane which passes through said beam and which is substantially parallel to the axis thereof, means for modulatingaportion ofsaid beam above said plane in accordance with a second signal, means for putting two additional modulations on'sald beam, one of said additional modulations being put on a portion of said beam located on one side of a substantially vertical plane and the other additional modulation being put on a portion of said beam on the other side of said verticalplane, receiving apparatus on said air craft, said apparatus including means for demodulating said beamportions whereby saidsignals and additional modulations appear in the output of said receiving apparatus, a visual indicating device having two pivotally mounted pointers so positioned that they intersect as they are moved through a certain angle, means for controlling the position of one of said pointers in accordance with-said first and second signals, and means for controlling the position of the other of said pointers in accordance with said additional modulations.

5. In a system for guiding an air craft, means for producing a beam of radiant energy at an angle to the vertical, means for modulating a portion of said beam in accordance with a first sighe], said portion being below a plane which passes through said beam and which is substantially parallel to the axis thereof, means for modulating a portion of said beam above said plane in accordance with a second signal, means for putting two additional modulations on said beam, one of said additional modulations being put on a portion of said beam located on one side of a'substantially vertical plane and the other additional modulation being put on a portion of said beam on the other side of said vertical plane, receiving apparatus on said air craft, said apparatus including means for demodulating said beam portions whereby said signals and additional modulations appear in the output of said receiving apparatus, a visual indicating device having a pointer pivotally mounted to move to either side of a horizontal line and a pointer pivotally mounted to move to either side of a vertical line, said pointers being so positioned that they intersect as they are moved through a certain angle, means for controlling the position of said first pointer in accordance with said first and second signals, and means for controlling the position of said second pointer in accordance with said additional modulations.

6. In a system for guiding an air craft, means for projecting a beam of radiant energy over at least a portion of a landing field for said air craft and at an' angle thereto, means for modulating the upper portion of said beam in accordance with one signal, means for modulating the lower portion of said beam in accordance with another signal, receiving apparatus on said air craft including means for demodulating said beam portions whereby said two signals appear in the output of said receiving apparatus, an instrument comprising a horizon bar and an indicator, said indicator being below said bar when the nose of said air craft is pointed downward, a vertically movable indicator, a fixed reference point for said indicator, means for moving said indicator above said point in response to said one signal, and meansior moving said indicator below said point in response to said other signal.

7. In a signalling system, meansior producing a beam of electromagnetic energy having a frecraft andat an acute angle thereto, means for modulating one portion of said beam in accordance with one signal, means for modulating another portion of said beam in accordance with a ,dlfierent signal, one ofisaid portions being 1oeated adjacent the other of said portions, means relatively positioning the first and second modulati'ng means whereby one of said means modulates the upper portion of said beam and while the other modulates the lower portion of said beam, and means for efiecting two additional modulations of said beam, one modulating one vertical portion of said beam and the other modulating an adjacent vertical portion of said beam.

EWING WQHFF. 

